Mac Mail. Coordinating on both computers

I use POP email on several computers with the following settings:

1. all outgoing messages are automatically bcc to me - a standard Mail setting under Composing
2. all accounts are set to keep mail on the server for 122 days - 4 months

Provided I use each computer at least once in the 4 months this has the following advantages:

1. all computers are the same and have access to all outgoing emails - see note
2. I can see if outgoing mail delivery is slow or has a problem
3. all mail is backed up on several computers

The only downside is extra incoming mail but I am happy with this.

Note: My main email client is TenFourBird which has a simple archive facility which helps me store all email over a day old in year folders - one folder per year. I don't have any other mail folder structure so this ensures that all computers have the some email folder structure.